A gear transmission is known that comprises an eccentric rotation gear configured to rotate eccentrically, and a rotation gear meshing with the eccentric rotation gear and comprising a different number of teeth from a number of teeth of the eccentric rotation gear. In this type of gear transmission, the eccentric rotation gear is rotated eccentrically by using a crankshaft. A through hole is provided in the eccentric rotation gear, and an eccentric portion is provided on the crankshaft. The eccentric portion is disposed in the through hole of the eccentric rotation gear. A bearing (called first bearing below) is disposed between the eccentric portion and the through hole. In a gear transmission of Japanese Patent Application Publication No. H5-180278 (1993), a washer is attached to a shaft portion of the crankshaft, regulating movement of the first bearing in an axial direction of the first bearing.